AMG 416 is a synthetic, eight amino-acid selective peptide agonist of the calcium sensing receptor. It is being developed as an intravenous treatment of secondary hyperparathyroidism (SHPT) in hemodialysis patients with chronic kidney disease-mineral and bone disorder (CKD-MBD).
The hydrochloride salt of AMG 416 has the chemical structure:

The main chain has 7 amino acids, all in the D-configuration. The side-chain cysteine residue is in the L-configuration. The molecular formula of AMG 416 (free base) is C38H73N21O10S2, and has a calculated average molecular mass of 1048.3 Da.
AMG 416 and a method for its preparation are described in International Pat. Publication No. WO 2011/014707, which is incorporated herein by reference for any purpose. As described in International Pat. Publication No. WO 2011/014707, AMG 416 may be assembled by solid-phase synthesis from the corresponding Fmoc-protected D-amino acids. After cleavage from the resin, the material may be treated with Boc-L-Cys(NPyS)—OH to form the disulfide bond. The Boc group may then be removed with trifluoroacetate (TFA) and the resulting product purified by reverse-phase high pressure liquid chromatography (HPLC) and isolated as the TFA salt form by lyophilization. The TFA salt can be converted to a pharmaceutically acceptable salt by carrying out a subsequent salt exchange procedure. Such procedures are well known in the art and include, e.g., an ion exchange technique, optionally followed by purification of the resultant product (for example by reverse phase liquid chromatography or reverse osmosis).
There is a need for an efficient method of producing AMG 416, or a pharmaceutically acceptable salt thereof (e.g., AMG 416 HCl), and particularly one appropriate for commercial scale manufacturing.